The preferred embodiment concerns a method and a device for control of a printer or copier, in which a series of discrete signal states are generated with whose help a drive unit for conveying a carrier material to be printed is controlled. A control signal for ending the conveying of the carrier material is generated. The series of the discrete signal states is at the earliest changed as of the signal state change following the control signal due to the stop signal. The signal state change of the series of discrete signal states that follows the control signal is thereby generated in the series provided before the control signal. The control signal thus has an effect only after the next signal state change providing the original signal series. A reaction to the stop signal thereby only occurs as of the next signal state change. No reaction to the stop signal thus occurs in the intervening time between the control signal and the signal state change following the control signal.
In particular in the printing of web-shaped paper webs, start/stop events of the paper web in which the paper web is halted is applicable retracted and accelerated before a new transfer printing event are necessary in the generation of a plurality of print images in succession, whereby the subsequent print image is either printed congruently over a previously printed print image or bordering on a previously printed print image. If a second print image should subsequently be generated on the paper web or be generated bordering a first, previously printed print image, it is desirable that the leading edge of the second print image abuts directly on the trailing edge of the first print image. A stop event of the paper web occurs after the first print image and a start event occurs before the second printing process, in which start event the individual components of the printer or copier (such as electrophotography, paper transport, fixing station, character generator etc.) must be synchronized with one another such that the subsequent print image to be generated is correctly positioned on the paper.
The start and stop processes are controlled with the aid of a control unit. In particular what is known as a trans-run signal is generated that predetermines the start and the end of an image generation process with the aid of a character generator, such that various further control units or sub-control units of the printer or copier can be synchronized with the aid of the trans-run signal. For example, the falling edge of the trans-run signal characterizes the beginning of a print image output by the character generator, i.e. the point in time at which the character generator begins to generate the first line of a latent print image. The character generator subsequently generates a print image with n page length line-by-line on a photoconductor, for example on a photoconductor drum or on an OPC band. The latent print image generated on the photoconductor in the form of a charge image with the aid of the character generator is preferably inked with toner material into a toner image that is subsequently transferred onto a transfer band.
With the aid of the transfer band, the toner image is transported to a transfer printing location at which it is transferred onto the paper web. The time from generation of a print image line with the aid of the character generator to the transfer of this line of the print image (which line is inked with toner material) onto the paper web is dependent on the geometry and design of the respective printer, however can be determined exactly for each printer or copier. Such a line of a print image is also designated as a μ-line of the print image.
Due to the known time between generation of a line of the print image with the aid of the character generator to the transfer-printing of this line on the paper web, the paper web is time-accurately accelerated to transfer printing speed with the aid of a paper transport device or a paper conveyance device before the arrival of the first line of the print image. The contact between the transfer belt and the paper web is preferably only generated at the moment in which the first μ-line of a print image to be transfer-printed arrives at the transfer printing location. The position of the paper web is thereby controlled such that the first μ-line of the print image impacts a position of the top of a page of the paper web. This top of a page preferably lies immediately at the end of a previous print image generated on the paper web, such that the trailing edge of the previously generated print image immediately borders the μ-line of the currently generated print image.
If no further position data is supplied to the printer for at least a short time and upon generation of a plurality of color separations to be printed on top of one another in multi-color printing, the paper web must be halted for at least a short time. A rising edge of the trans-run signal signals the end of the print image output by the character generator, whereby the rising edge of the trans-run signal is generated at the moment at which the character generator has completely generated the last μ-line of the print image to be generated. Based on the rising edge of the trans-run signal, a timer is started with a predetermined time period that is required from the generation of the last print image line with the aid of the character generator to the transfer of this line inked with toner material onto the paper web.
With the expiration of the timer, a control signal is generated via which the transfer band is raised from the paper web and the conveying event is subsequently stopped. The acceleration and stoppage of the paper web occurs with the aid of what are known as acceleration ramps via which the drive unit for driving the paper web is controlled such that the paper web is essentially uniformly accelerated and uniformly braked. The paper web is essentially driven with constant speed from the point in time of the transfer of the first line of a print image to the transfer of the last line of a print image.
After the transfer printing of the last line of a print image, a uniform braking of the paper web to a stop occurs, whereby the paper web is uniformly negatively accelerated. A retraction of a paper web subsequently occurs, whereby the paper web is conveyed a preset distance counter to the conveying direction in the printing of the paper web. This distance comprises the distance conveyed after the control signal for stopping the paper web up to the standstill of the paper web and furthermore the distance required for the subsequent acceleration of the paper web during a subsequent transfer printing process for acceleration of a subsequent print image. This required distance serves to accelerate the paper web to transfer printing speed upon arrival of the first μ-line of the subsequent print image at the transfer printing location.
Positioning systems for paper webs that can only be positioned stably in discrete steps are in particular used in electrophotographic printers or copiers. These steps are, for example, half-steps given the use of step motors or decoder increments given servomotors.
Given some predetermined page lengths, the problem thereby arises that, given a print stop at the point in time at which the last μ-line has been transfer-printed onto the paper web, this does not coincide with the end or with the beginning of a discrete step of the positioning system. After a stop event in which the paper web is uniformly braked to a standstill and after the retraction of the paper web after this stop event, a false positioning of the paper web by a maximum of one step is thus possible since the paper web has been transported by a maximum of one step too far. Given the transfer printing of a subsequent print image to be generated, the desired top of the page of the paper web reaches the transfer printing location before the first line of the print image to be transfer-printed, such that a gap is created between the two print images to be generated in succession or the pages to be printed in succession.
In known printers or copiers for printing of web-shaped paper webs, the possible page length to be preset would be limited to pages in which the smallest common multiple of character generator resolution, raster precision in the controller and paper transport position raster would be formed that serves as a raster for setting a possible page length. In the following table, the determination of the raster for possible page lengths to be set is shown for two printers selected as examples.
Printer 1Printer 2Character generator 1/600 inch 1/600 inchresolutionper μ-lineper μ-lineRaster precision 1/600 inch 1/300 orin the controllerper μ-line 1/600 inchper μ-linePaper transport 1/90 inch 1/120 inchpositioning rasterper motor half-stepper motor half-stepRaster for page 1/30 1/60lengthinch = 0.847 mminch = 0.4235 mm
In the prior art, the possible page lengths to be printed amount to a multiple of these determined rasters. The print images can in fact thereby be positioned exactly, however the spectrum of the selectable page lengths and thus also the application spectrum of the printer or copier is thereby limited.
The use of a step motor for driving a recording medium in an electrophotographic printer or copier is known from the document U.S. Pat. No. 5,172,180, in which different hold positions of the medium result after the generation of a color separation. For synchronization of the color separations, a position marker is provided whose position is detected with the aid of a sensor. It is thereby achieved that the position deviation of the medium comprises a half-step or one step of the step motor.
An image generation device and a method for control of the image generation device is known from the document US 2004/0013451, in which in particular three timers are provided in order to generate three different stop positions of an endless belt, i.e. of a photoconductor belt or a transfer belt.
From the subsequently published document EP 1 496 404 A1, an image generation device with a drive controller is known in which a deviation of the actual drive speed from a desired drive speed of a step motor is prevented, in particular in the acceleration of the step motor.